[Feature] Add support for XDG.

[Akilan1999]

XDG

• The XDG Base Directory Specification is based on the following concepts:

• There is a single base directory relative to which user-specific data files should be written. This directory is defined by the environment variable $XDG_DATA_HOME.

• There is a single base directory relative to which user-specific configuration files should be written. This directory is defined by the environment variable $XDG_CONFIG_HOME.

• There is a single base directory relative to which user-specific state data should be written. This directory is defined by the environment variable $XDG_STATE_HOME.

• There is a single base directory relative to which user-specific executable files may be written.

• There is a set of preference ordered base directories relative to which data files should be searched. This set of directories is defined by the environment variable $XDG_DATA_DIRS.

• There is a set of preference ordered base directories relative to which configuration files should be searched. This set of directories is defined by the environment variable $XDG_CONFIG_DIRS.

• There is a single base directory relative to which user-specific non-essential (cached) data should be written. This directory is defined by the environment variable $XDG_CACHE_HOME.

• There is a single base directory relative to which user-specific runtime files and other file objects should be placed. This directory is defined by the environment variable $XDG_RUNTIME_DIR.

• All paths set in these environment variables must be absolute. If an implementation encounters a relative path in any of these variables it should consider the path invalid and ignore it.

source: https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html

[Akilan1999]

https://github.com/adrg/xdg (We can use this repo for following XDG specifications).
This would mean the base directories would be generated on the XDG paths and pointed on the Config files.